Object capturing device

ABSTRACT

An object capturing device configured to capture an object present in a measurement target space includes a light emission unit, a light receiving unit, a light scanning unit configured to cause measurement light emitted at a predetermined wavelength from the light emission unit to head toward a measurement target space to perform scanning, and to guide reflected light from an object present in the measurement target space with respect to the measurement light to the light receiving unit, and a polarization filter disposed in the light scanning unit, the polarization filter including a polarizer configured to allow only light vibrating in a first direction in the measurement light to transmit, and an analyzer configured to allow only light vibrating in a second direction perpendicular to the first direction in the reflected light to transmit.

This application is based on an application No. 2017-027778 filed inJapan, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an object capturing device configuredto capture a certain object from among objects present in a measurementtarget space.

DESCRIPTION OF THE RELATED ART

In a manufacturing facility for semiconductor devices, carrying cartsare used to convey wafer carrier devices each accommodating a pluralityof semiconductor wafers from a loading port of a manufacturing device toa loading port of another manufacturing device. Such a carrying cart isreferred to as a ceiling-traveling type automated guided vehicle, oroverhead hoist transfer (OHT).

To avoid each of the carrying carts from coming into contact with anobstruction, such as a person or a machine, the carrying carts eachinclude a traveling section configured to autonomously travel along atraveling rail defining a route, which is arranged in a space abovemanufacturing devices, and an item accommodating section being supportedby the traveling section. The item accommodating section is assembledwith a lifting and lowering mechanism configured to lift and lower,along a predetermined lifting and lowering passage, a lifted and loweredmember provided with a chuck mechanism configured to grab each of thewafer carrier devices representing conveyance target objects.

To convey the wafer carrier devices in accordance with a layout of themanufacturing devices, the route has a complex shape including not onlysimple straight portions, but also curves, branched portions, andmerging portions, for example. The manufacturing facility is constructedto allow the plurality of carrying carts to travel at intervals on theroute.

To increase efficiency in conveying wafer carrier devices, many carryingcarts have been demanded to travel at higher speeds on the route in themanufacturing facility. Since, to achieve this demand, inter-vehiculardistances between carrying carts have been prone to be shorter, such amechanism is necessary that prevents contingent collisions fromoccurring.

Patent document 1 discloses such a technique that carrying carts areeach provided with an inter-vehicular distance sensor, such as a laserrange finder, to avoid the carrying carts from colliding with eachother. Based on an inter-vehicular distance measured by theinter-vehicular distance sensor, a relative speed to another proceedingone of the carrying carts is calculated. Based on the relative speed, atravel speed of each of the carrying carts is controlled to avoid acollision.

However, since, in such a case where a proceeding carrying cart travelsa curve on the route, the proceeding carrying cart disappears from ascanning range of measurement light output from the laser range finder,this case may result in that not only the proceeding carrying cartcannot be detected, but also reflected light from, for example, anexterior panel of a manufacturing device or another traveling cart iserroneously detected as reflected light from the proceeding carryingcart.

To solve this problem, Patent document 2 proposes a distance measurementdevice that includes, at a front section of a carrying cart configuredto travel along a route, a ranging device including a scanner configuredto perform scanning in a plane shape with measurement light beingmodulated, and a distance calculation unit configured to calculate adistance to an object to be detected based on a time delay between themeasurement light used for scanning by the scanner and reflected lightfrom the object to be detected, and that is configured to detect, basedon reflected light, which is detected by the ranging device, from arecursive reflecting member disposed at a rear section of a proceedingcarrying cart, an inter-vehicular distance between the carrying carts.

The distance measurement device includes an identifying unit configuredto identify whether reflected light from the recursive reflecting memberis received based on an interrelationship between at least two out of aplurality of scanning angles of measurement light used for scanning bythe scanner, distances that correspond to the scanning angles and thatare calculated by the distance calculation unit, and values of intensityof reflected light, which correspond to the scanning angles.

PRIOR ART DOCUMENT

[Patent document 1] Japanese Unexamined Patent Application PublicationNo. 2007-25745

[Patent document 2] Japanese Unexamined Patent Application PublicationNo. 2011-69671

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, even the distance measurement device described in Patentdocument 2 could not completely eliminate to misidentify reflected lightfrom a wall surface of a manufacturing device as reflected light fromthe recursive reflecting member mounted on the carrying cart.

One reason is that, depending on a distance of separation between thedistance measurement device and a wall surface irradiated withmeasurement light, reflection properties of the wall surface irradiatedwith the measurement light are similar to reflection properties of therecursive reflecting member disposed at the rear section of the carryingcart. Such a case corresponds to, for example, a case where a wallsurface is made from a metal plate made of aluminum or other metals andmeasurement light is incident on the wall surface in a substantiallyvertical direction, or a case where a wall surface is an embossed, whitepainted surface.

In the cases described above, such an extremely burdensome separateadjustment on an interrelationship serving as a reference fordetermination is required per manufacturing facility to avoid erroneousdeterminations.

Similar problems can occur in not only ceiling-traveling type automatedguided vehicles and OHTs described above, but also carrying carts eachconfigured to be guided to a plurality of landmarks disposed along atraveling passage to travel in an automated manner to a destinationwithout being departed from the traveling passage. Such a carrying cartis collectively referred to as an automated guided vehicle (AGV).

An AGV is equipped with a distance measurement device configured to scanlandmarks disposed along a passage by measurement light to detectreflected light from recursive reflecting members respectivelyconstituting the landmarks and to confirm a position or to detect anobstruction, such as a person or an object, present on the travelingpassage.

Even such an AGV, however, may deviate from the traveling passage whenreflected light from a wall surface of a manufacturing device, forexample, is erroneously determined as reflected light from one of thelandmarks.

In view of the problems described above, the present invention has anobject to provide an object capturing device capable of determiningwhether an object is a capture target.

Means For Solving the Problems

A first characteristic configuration of an object capturing deviceaccording to the present invention is, as described in claim 1 in theappended claims, an object capturing device configured to capture anobject present in a measurement target space, and including a lightemission unit, a light receiving unit, a light scanning unit configuredto cause measurement light emitted at a predetermined wavelength fromthe light emission unit to head toward a measurement target space toperform scanning, and to guide reflected light from an object present inthe measurement target space with respect to the measurement light tothe light receiving unit, and a polarization filter disposed in thelight scanning unit, the polarization filter including a polarizerconfigured to allow only light vibrating in a first direction in themeasurement light to transmit, and an analyzer configured to allow onlylight vibrating in a second direction perpendicular to the firstdirection in the reflected light to transmit.

In measurement light emitted from the light emission unit, only linearlypolarized light vibrating in the first direction is allowed to transmitthe polarizer for scanning in a measurement target space. Meanwhile, inreflected light from an object, only linearly polarized light vibratingin the second direction perpendicular to the first direction is allowedto transmit the analyzer, and is guided to the light receiving unit.With the light scanning unit provided with the polarizer and theanalyzer, neither measurement light along scanning nor reflected lightchange in polarization direction. With such reflection properties of areflection surface of a capture target that cause a polarizationdirection of measurement light to rotate 90 degrees, the capture targetcan be surely identified.

A second characteristic configuration of the object capturing deviceaccording to the present invention is that, as described in claim 2 inthe appended claims, in addition to the first characteristicconfiguration described above, a circular polarizing plate may bedisposed between the light emission unit and the polarizer.

By allowing measurement light to pass through the circular polarizingplate to be circularly polarized, and then to be incident on thepolarizer, linearly polarized light vibrating in the first direction canbe easily obtained. As a result, such an adjustment is not required, ona relative positional relationship between the light emission unit andthe polarizer, that of allowing a polarization direction of linearlypolarized light in light emitted from the light emission unit and apolarization direction by the polarizer to align with each other.

A third characteristic configuration of the object capturing deviceaccording to the present invention is that, as described in claim 3 inthe appended claims, in addition to the second characteristicconfiguration described above, a second polarizer may be disposedbetween the light emission unit and the circular polarizing plate.

By adjusting the second polarizer to allow a polarization surface toreceive incident light at a bearing angle of 45 degrees relative to afast axis or a slow axis of the circular polarizing plate, linearlypolarized light can turn into circularly polarized light forming asubstantially perfect circle. As a result, with the polarizer providedin the light scanning unit, measurement light appropriately linearlypolarized can be obtained.

A fourth characteristic configuration of the object capturing deviceaccording to the present invention is that, as described in claim 4 inthe appended claims, in addition to any one of the first to thirdcharacteristic configurations described above, the light scanning unitmay include a deflecting mirror and a light guide unit defining anoptical path configured to guide measurement light deflected by thedeflecting mirror to the measurement target space and an optical pathconfigured to guide the reflected light to the light receiving unit.Furthermore, the polarizer may be disposed on a measurement lightoptical path side of the light guide unit. Meanwhile, the analyzer maybe disposed on a reflected light optical path side of the light guideunit.

The light guide unit defines regions of optical paths into themeasurement light optical path and the reflected light optical path.When measurement light emitted from the light emission unit travelsthrough the measurement light optical path, only linearly polarizedlight vibrating in the first direction passes through the polarizer toreach a measurement target space to achieve scanning. When reflectedlight from an object advances into the reflected light optical path,only linearly polarized light vibrating in the second directionperpendicular to the first direction passes through the analyzer. Thereflected light is then received by the light receiving unit.

A fifth characteristic configuration of the object capturing deviceaccording to the present invention is that, as described in claim 5 inthe appended claims, an object capturing device configured to capture anobject present in a measurement target space includes a light emissionunit, a light receiving unit, and a light scanning unit to transmitmeasurement light emitted at a predetermined wavelength from the lightemission unit toward a measurement target space, and to guide reflectedlight from an object present in the measurement target space withrespect to the measurement light to the light receiving unit. The lightscanning unit includes a light guide unit defining an optical pathconfigured to guide measurement light deflected by the deflecting mirrorto the measurement target space and an optical path configured to guidethe reflected light to the light receiving unit and a half mirrordisposed on a measurement light optical path side of the light guideunit configured to guide the reflected light to the light receivingunit.

In a case where the half mirror is not provided, and an object to beirradiated with measurement light lies adjacent to the objectdetermination device, a diameter of a measurement light beam emittedfrom the light guide unit reduces. As well as a degree of expansion of areflected light beam from the object reduces. As a result, a diameter ofreflected light beam advancing in the reflected light optical pathbecomes closer to a diameter of measurement light advancing in themeasurement light optical path. As well as, a quantity of light guidedto the light receiving unit reduces. In this case, such a situation mayoccur that a distance is not precisely detected. Even in a case, byproviding a half mirror, reflected light from the object is reflected bythe half mirror, and is guided to the light receiving unit 22. As aresult, even an adjacent object can be precisely detected.

A sixth characteristic configuration of the object capturing deviceaccording to the present invention is that, as described in claim 6 inthe appended claims, in addition to any one of the first to fifthcharacteristic configurations described above, the object capturingdevice may include a casing. A part of the casing serving as a path forthe measurement light and the reflected light is made of a materialwhich transmits the measurement light and has low polarizationproperties with respect to the measurement light.

By using a material having low polarization properties, as a materialconstituting a part of the casing, which serves as a path formeasurement light and reflected light, i.e., an optical window,properties of polarizing measurement light and reflected light passingthrough the optical window can be suppressed from changing, avoidingdetection accuracy from lowering.

A seventh characteristic configuration of the object capturing deviceaccording to the present invention is that, as described in claim 7 inthe appended claims, in addition to any one of the first to sixthcharacteristic configurations described above, the light emission unitmay include a plurality of light sources configured to emit light atdifferent wavelengths, the light emission unit being switched and drivenin synchronization with a scanning period of the light scanning unit.

The plurality of light sources configured to emit light at differentwavelengths are switched and driven in synchronization with a scanningperiod of the light scanning unit. During at least one scanning period,scanning is performed with measurement light at a constant wavelength.During the one scanning period, the wavelength of the measurement lightdoes not change.

Effects of Invention

As described above, according to the present invention, an objectcapturing device capable of determining whether an object is a capturetarget can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a manufacturing facility forsemiconductor devices and carrying carts configured to move along atraveling rail.

FIG. 2 is a diagram illustrating processing of transferring wafercarriers among the carrying carts and manufacturing devices.

FIG. 3 is a perspective view of one of the carrying carts.

FIG. 4 is a functional block diagram illustrating a conveyance controlunit mounted on each of the carrying carts.

FIGS. 5A, 5B, and 5C are diagrams each illustrating a positionalrelationship of two of the carrying carts configured to move along thetraveling rail.

FIG. 6 is a diagram illustrating an appearance of an object capturingdevice.

FIG. 7 is a diagram illustrating an internal structure of the objectcapturing device.

FIG. 8 is a functional block diagram illustrating a control unitassembled in the object capturing device.

FIGS. 9A, 9B, and 9C are diagrams each illustrating an interrelationshipbetween a distance and a scanning angle range.

FIGS. 10A, 10B, and 10C are diagrams each illustrating aninterrelationship between a distance and intensity distribution ofreflected light.

FIGS. 11A, 11B, and 11C are diagrams each illustrating aninterrelationship between reflection properties of a reflecting sheetand intensity distribution of reflected light.

FIG. 12 is a flowchart illustrating an operation of an objectdetermination unit.

FIGS. 13A and 13B are diagrams each illustrating a recursive reflectingmember used as a reflecting sheet.

FIG. 14 is a diagram illustrating an internal structure of an objectcapturing device according to still another embodiment.

FIG. 15 is a diagram illustrating an internal structure of an objectcapturing device according to still another embodiment.

FIG. 16 is a diagram illustrating an internal structure of an objectcapturing device according to still another embodiment.

FIG. 17A is a diagram of properties of detecting reflected light withrespect to a plurality of reflecting members. FIG. 17B is a diagram ofproperties of detecting reflected light with respect to a change inangle of a reflecting plate. FIG. 17C is diagram of properties ofdetecting reflected light with respect to a scanning direction. FIG. 17Dis a diagram of properties of detecting reflected light with respect toa scanning direction in a case where an angle of a reflecting plate ischanged.

FIG. 18 is a diagram illustrating materials of the reflecting plates(reflecting members).

FIGS. 19A and 19B are diagrams each illustrating reflection propertiesof a reflecting sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Here will describe an embodiment where an object capturing systemassembled with an object capturing device according to the presentinvention is applied to each of automated carrying carts provided in amanufacturing facility for semiconductor devices.

As illustrated in FIG. 1, a manufacturing facility 100 for semiconductordevices includes various manufacturing devices 1 (1 a to 11) that arearranged along a predetermined route and that sequentially executepredetermined processing on semiconductor wafers, a traveling rail 5suspended from a ceiling in such a manner as to extend along themanufacturing devices 1, and a plurality of carrying carts (OHTs) 10that travel along the traveling rail 5 to automatically conveysemiconductor wafers W among the manufacturing devices 1 (1 a to 11).The manufacturing devices 1 (1 a to 11) are separately provided in bays6 and 7 per a series of manufacturing steps. Wafer carriers 3 eachaccommodate the plurality of semiconductor wafers W.

The traveling rail 5 includes not only simple straight portions, butalso curves, branched portions, and merging portions, for example. Forexample, the traveling rail 5 includes inter-step rails 5 a respectivelycoupling the bays 6 and 7, in-step rails 5 b respectively coupling themanufacturing devices 1 in the bays 6 and 7, branched rails 5 crespectively coupling the inter-step rails 5 a and the in-step rails 5b, side rails 5 d with which the carrying carts 10 running on thein-step rails 5 b are sidetracked, and bypass rails 5 e with which thecarrying carts 10 respectively pick up or load the wafer carriers 3 onstockers ST.

The branched rails 5 c respectively couple the inter-step rails 5 a andthe in-step rails 5 b, allowing the carrying carts 10 to travel alongthe branched rails 5 c to move back and forth among the inter-step rails5 a and the in-step rails 5 b.

The side rails 5 d are respectively branched from the in-step rails 5 b,and are used for temporarily sidetracking the carrying carts 10 from thein-step rails 5 b for allowing the carrying carts 10 to undergomaintenance services, for example.

The bypass rails 5 e are respectively branched from the inter-step rails5 a, and are used for a case where one of the wafer carriers 3, which isheld by one of the carrying carts 10 traveling on the inter-step rails 5a, is to be temporarily stored on one of the stockers ST.

As illustrated in FIGS. 2 and 3, the traveling rail 5 is suspended fromthe ceiling by support members 11 at appropriate intervals, and is madefrom a pipe shaped member having a rectangular cross-sectional shapeformed, on its lower wall, with a slit 5A having a slit shape extendingin a longitudinal direction. The carrying carts 10 each include atraveling section 10A that travels along an upper surface 5B of an innerside of the lower wall of the pipe shaped member while sandwiching theopening 5A, and a holding section 10B that is coupled with the travelingsection 10A with a coupling member 10D and positioned below the lowerwall of the pipe shaped member.

The traveling section 10A includes a traveling base and a front-rearpair of wheels attached to the traveling base, as well as is mountedwith, for example, a conveyance control unit configured to control atraveling motor configured to drive the wheels and a lifting andlowering mechanism 10E described later to convey each of the wafercarriers 3 to a target one of the manufacturing devices 1.

FIG. 4 illustrates a functional block configuration of a conveyancecontrol unit 70 mounted on each of the carrying carts 10. The conveyancecontrol unit 70 includes a traveling control unit 71 including amicrocomputer and its peripheral circuits, a chuck mechanism controlunit 72 coupled to the traveling control unit 71, a host communicationunit 73, and an optical communication unit 10F, for example.

Based on an instruction from a system controller H (see FIG. 1), theconveyance control unit 70 performs a control to hold one of the wafercarriers 3 placed on one of loading ports 2 of the manufacturing devices1 (1 a to 11), to travel among the manufacturing devices 1 or among thestockers ST each configured to temporarily store the wafer carriers 3,and to place the one of the wafer carriers 3 on a destination ofconveyance, i.e., another one of the loading ports 2.

The holding section 10B is assembled with a lifted and lowered member10D including a chuck mechanism 10C configured to hold one of the wafercarriers 3, and the lifting and lowering mechanism 10E including a beltand a winding motor configured to lift and lower the lifted and loweredmember 10D along a predetermined lifting and lowering passage.

On a bottom surface of the holding section 10B, the opticalcommunication unit 10F configured to locally communicate with an opticalcommunication unit 2C provided in each of the manufacturing devices 1 isassembled. After arrival at a position adjacent to a target one of themanufacturing devices 1 based on an instruction from the systemcontroller H, when recognizing that an optical communication has beenestablished between the optical communication units 2C and 10F, thetraveling control unit 71 performs a control to stop the travelingmotor. A signal transmission medium for local communications may be aradio communication medium, and may use radio waves, for example,instead of light. That is, instead of the optical communication unit, awireless communication unit may be used.

Furthermore, when the winding motor is controlled to lower the liftingand lowering mechanism 10E, and a holding motor configured to be drivenvia the chuck mechanism control unit 72 is caused to hold one of thewafer carriers 3, the winding motor is controlled to lift the liftingand lowering mechanism 10E, and the one of the wafer carriers 3 isconveyed to a destination of conveyance, i.e., one of the manufacturingdevices 1, for example.

As illustrated in FIG. 3, in the holding section 10B, an objectcapturing device 20 is assembled on a front surface side in a travelingdirection of each of the carrying carts 10, and a reflecting sheet 40having a predetermined size is applied on a rear surface side in thetraveling direction.

As illustrated in FIGS. 5A to 5C, the object capturing device 20 isconfigured to emit measurement light forward, i.e., in an advancingdirection, to perform scanning, to detect reflected light from areflecting sheet 40F applied on a proceeding carrying cart 10F, tocalculate an inter-vehicular distance to the proceeding carrying cart10F, and to output the calculated inter-vehicular distance to theconveyance control unit 70 (traveling control unit 71). When determiningthat an inter-vehicular distance input from the object capturing device20 is shorter than an allowable value, the conveyance control unit 70performs a control to cause a corresponding one of the carrying carts 10to decelerate or stop to avoid collision. Such a control unit may beprovided in the object capturing device 20 that is configured to outputa control signal controlling and causing each of the carrying carts 10to decelerate or stop to avoid collision.

In a case where another proceeding carrying cart enters, from a straighttraveling rail, as illustrated in FIG. 5A, a curved traveling rail, asillustrated in FIG. 5B, if reflected light from a panel, for example, ofone of the manufacturing devices 1, which is mounted on a line extendingfrom a portion immediately before the curved portion of the travelingrail 5, as illustrated in FIG. 5C, is erroneously detected as reflectedlight from the reflecting sheet 40F applied on the proceeding carryingcart 10F, and a corresponding one of the carrying carts 10 is caused todecelerate or stop, the corresponding one of the carrying carts 10 facesdifficulty in restarting traveling from the stopped state. To preventsuch an event, the object capturing device 20 is provided with an objectdetermination unit configured to determine whether reflected light beingdetected is reflected light from the reflecting sheet 40F applied on aproceeding carrying cart.

The object capturing device 20 will be described herein in detail.

[Object Capturing Device According to First embodiment]

FIG. 6 illustrates an appearance of the object capturing device 20. FIG.7 illustrates an internal structure of the object capturing device 20.As illustrated in FIG. 6, the object capturing device 20 includes alower casing 20A having a substantially rectangular parallelepipedshape, and an upper casing 20B provided with an optical window 20Chaving a substantially cylindrical shape. The lower casing 20A isfurther provided with a signal coupling section CN and a display section20D.

As illustrated in FIG. 7, the casings 20A and 20B of the objectcapturing device 20 accommodate a light emission unit 21, a lightreceiving unit 22, a light scanning unit 23, a light projection lens 24,a light receiving lens 25, and signal processing substrates 30 and 31.

The light scanning unit 23 includes a motor 50 provided on an inner wallof an upper surface of the upper casing 20B, and a deflecting mirror 52that is fixed to a rotating shaft 51 of the motor 50 and that isintegrally rotatable with the rotating shaft 51. The deflecting mirror52 is set to have an inclination angle of 45 degrees relative to therotating shaft 51. Furthermore, the rotating shaft 51 is provided withan encoder 53 configured to measure a rotational speed of the motor 50.The encoder 53 functions as a scanning angle detection unit with respectto measurement light.

On an optical axis P concentric with the rotating shaft 51 disposed in aperpendicular posture, as well as opposite to the motor 50 across thedeflecting mirror 53, the light receiving lens 25 and the lightreceiving unit 22 are disposed at positions different from each other inupper and lower directions. At a central part of the light receivinglens 25, an opening part cut out into a cylindrical shape is formed. Ata lower end of the opening part, the light emission unit 21 is disposed.Above the lower end, the light projection lens 24 is disposed.

A light guide unit 54 that is configured to integrally rotate with thedeflecting mirror 52 and that defines a measurement light optical pathL1 configured to guide measurement light deflected by the deflectingmirror 52 to a measurement target space and a reflected light opticalpath L2 configured to guide reflected light deflected by the deflectingmirror 52 to the light receiving unit 22 is fixed to the deflectingmirror 52 to be allowed to integrally rotate with the deflecting mirror52.

The light emission unit 21 includes an infrared laser diode that ismounted on a substrate supported in a cantilever manner. After coherentmeasurement light emitted from the laser diode is formed into parallellight by the light projection lens 24, is incident on the deflectingmirror 52 along the optical axis P, and is deflected at an angle of 90degrees, the measurement light passes through an inside region, i.e.,the measurement light optical path L1, defined by the light guide unit54 along the optical axis P1, and is emitted from the optical window 20Cto a measurement target space.

A surface of an object present in the measurement target space isirradiated with the measurement light. After part of its reflected lightenters from the optical window 20C along the optical axis P1, passesthrough an outside region, i.e., the reflected light optical path L2,defined by the light guide unit 54, becomes incident on the deflectingmirror 52, and is deflected by the deflecting mirror 52 at an angle of90 degrees, the light is concentrated by the light receiving lens 25,and becomes incident on the light receiving unit 22.

As for the light receiving lens 25, a flange part formed on itsperipheral part is supported by a lens holder 26. The substrateconstituting the light emission unit 21 is supported by the lens holder26. Furthermore, a substrate mounted with the light receiving unit 22and the signal processing substrates 30 and 31 are supported by aplurality of legs 27 supporting the lens holder 26.

Furthermore, in the light guide unit 54 assembled in the light scanningunit 23, at positions facing the optical window 20C, a polarizer PL isdisposed at an outlet end of the measurement light optical path L, andan analyzer AN is disposed at an inlet end of the reflected lightoptical path L2. That is, the polarizer PL is disposed inside of thelight guide unit 54, whereas the analyzer AN is disposed outside of thelight guide unit 54.

The polarizer PL causes only light vibrating in the first direction totransmit to the optical path for measurement light. The analyzer ANcauses only light vibrating in the second direction perpendicular to thefirst direction to transmit to the optical path for reflected light. Inthe light emission direction, at a position immediately behind the lightprojection lens 24, a ¼ wavelength plate 28 serving as an example of acircular polarizing plate is disposed.

A measurement light linearly polarized in a predetermined direction isemitted from the laser diode of the light emission unit 21 and passesthrough the ¼ wavelength plate 28 to turn into circularly polarizedlight. And the circularly polarized light further passes through thepolarizer PL to turn into linearly polarized light in a directionperpendicular to a scanning direction, for example.

As each of the polarizer PL and the analyzer AN, for example, such awire grid can be used that a fine metal grid is formed on a surface of aglass plate. Otherwise, such a crystalline material can be used thatutilizes a birefringence phenomenon of the material itself to adjustpolarized components.

By disposing, on a reflection surface of a capture target, such anoptical member that causes a polarization direction to rotate 90degrees, a polarization direction of reflected light rotates 90 degreesrelative to a polarization direction of measurement light. As such anoptical member, a recursive reflecting sheet arranged with a trihedroncube corner element or a ½ wavelength plate is preferably used.

FIG. 13A illustrates a trihedron cube corner element (also referred toas a microprism). Three reflecting mirrors 41, 42, and 43 perpendicularto each other constitute a unit element. Light that is incident on sucha trihedron cube corner element is reflected in an incident direction.

As illustrated in FIG. 13B, as measurement light passed through thepolarizer PL and being linearly polarized in a vertical direction isreflected by the three surfaces of the trihedron cube corner element,the measurement light turns into linearly polarized light in apolarization direction rotated 90 degrees. The linearly polarized lightthen passes through the analyzer AN.

Even when measurement light passed through the polarizer PL is reflectedby a metal plate made of aluminum, for example, reflected light does notchange its polarization direction. Accordingly, the reflected light doesnot pass through the analyzer AN. When measurement light passed throughthe polarizer PL is reflected by a white scatter plate, its polarizationdirection is disturbed. The measurement light then turns into reflectedlight where circularly polarized light and linearly polarized light indirections at various angles overlap with each other. As a result, aquantity of reflected light passing through the analyzer AN isapproximately halved.

As the polarizer PL and the analyzer AN included in the light scanningunit 23 rotate integrally with the deflecting mirror 52, neithermeasurement light emitted along scanning nor reflected light beingincident change in polarization direction. With such reflectionproperties of a reflection surface of a capture target that cause adeflecting direction of measurement light to rotate 90 degrees, thecapture target can be surely identified.

It is preferable that, to prevent polarization properties from changingeven when light passes through the optical window 20C, as a materialconstituting the optical window 20C serving as a passage for measurementlight and reflected light, such a material, as an acrylic resin oroptical glass having lower birefringence, be used that allowsmeasurement light to transmit and that has lower polarization propertieswith respect to measurement light.

The signal processing substrate 30 is provided with a control unit 80configured to control the object capturing device 20. The signalprocessing substrate 31 is mounted with light-emitting diodes (LEDs) anda liquid crystal display element respectively configured to displayvarious kinds of information on the display section 20D. The signalprocessing substrate 30, the light emission unit 21, and the lightreceiving unit 22 are coupled with each other via signal lines. From thesignal processing substrate 30, a signal cable configured to allowsignals to be exchanged, via the signal coupling section CN provided tothe lower casing 20A, with an external device extends.

FIG. 8 illustrates a functional block configuration of the control unit80. The control unit 80 includes a microcomputer and a digital signalprocessor, for example, and therefore includes a light emission controlunit 84 configured to control a light-emitting timing for the lightprojection unit 21, a distance calculation unit 81 configured tocalculate, based on a time difference or a phase difference betweenmeasurement light used for scanning by the light scanning unit 23 andreflected light from an object, a distance to the object to be detected,a correction calculation unit 83 configured to correct the distancecalculated by the distance calculation unit 81, and an objectdetermination unit 82.

A method for calculating a distance based on a time difference betweenmeasurement light and reflected light is referred to as a time-of-flight(TOF) method. A distance d is calculated with a mathematical expression1 described below. Where, C is a velocity of light, and ΔT is a timedifference.

d=(1/2)×C/ΔT   [Mathematical expression 1]

A method for calculating a distance based on a phase difference betweenmeasurement light that is emitted from a light source and that isallowed to undergo amplitude modulation (AM) at a predeterminedmodulation frequency and reflected light is referred to as an AM method,where a distance d is calculated with a mathematical expression 2described below. Where, φ is a measured phase difference, C is avelocity of light, and F is a modulation frequency of the light source.

d=(1/2)×(φ/2π)×C/F   [Mathematical expression 2]

The correction calculation unit 83 is a block configured to correct anerror due to variation in component of the object capturing device 20,for example, as well as is a functional block configured to obtain acorrection factor used to allow a distance calculated based on reflectedlight from a reference reflecting plate 55 provided on a part of theinner wall of the upper casing 20B to be a predetermined distance.

The description continues below with reference to an example where theTOF method is adopted. The description can also be applied to a casewhere the AM method is adopted.

The object determination unit 82 is configured to use a scanning angledetected by the scanning angle detection unit 53 and a distance obtainedby correcting with a correction factor calculated by the correctioncalculation unit 83 a distance calculated by the distance calculationunit 81 in accordance with the scanning angle (hereinafter will besimply referred to as a “distance calculated by the distance calculationunit 81”) to recognize a distance and a direction to a reflectionposition of measurement light, i.e., to the reflection position from theobject capturing device 20, to determine, based on a plurality of thereflection positions determined from the recognized distances and thedirections, whether a detected object is a capture target, as well as tooutput, when the detected object is the capture target, the distanceand/or the direction to the traveling control unit 71 of a correspondingone of the carrying carts 10.

Specification values of the object capturing device 20 described in thepresent embodiment are a detection distance ranging from 50 mm to 7000mm inclusive, a scanning angle range of 270 degrees, a scanning time of25 ms, and an angular resolution of 0.25 degrees. A lateral size and alongitudinal size of the reflecting sheet 40 are 300 mm and 270 mm,respectively. However, the specification values are mere examples. Thepresent invention does not intend to limit the specification values tothe values described above.

The object determination unit 82 is configured to recognize, as a sizealong a scanning direction of an object, a continuous scanning anglerange within which a difference in distance between a scanning anglecalculated by the distance calculation unit 81 and each of scanningangles adjacent to the scanning angle is determined to be equal to orless than a predetermined threshold value, and to determine whether anobject is a capture target based on a determination of whether thescanning angle range corresponds to a reference scanning angle range ofthe capture target, and whether intensity distribution of reflectedlight within the scanning angle range corresponds to reference intensitydistribution of reflected light from the capture target.

The reference scanning angle range of a capture target refers to ascanning angle range corresponding to a reference distance representingdistances calculated within the scanning angle range. As the referencedistance, a minimum distance and a maximum distance from the objectcapturing device 20 to an object, as well as a central value and anaverage value, for example, can be used. In the present embodiment, anaverage value is used.

As illustrated in FIG. 9A, in a case where the distance d calculated ata scanning angle θ by the distance calculation unit 81 and distancescalculated at scanning angles θ±Δθp (Δθp=0.25 degrees) adjacent to thescanning angle θ are each equal to or less than a predeterminedthreshold value Δd, objects corresponding to the distance d aredetermined as an identical object.

When a scanning angle range ±Δθ corresponding to a size of an objectalong a scanning direction corresponds to a reference scanning anglerange θ_(ref) of a capture target, which is set based on a referencedistance d_(ref) representing the distances d within the scanning anglerange ±Δθ, the detected object can be identified as the capture target.

That is, in a case where the reflecting sheet 40 lies at a position awayat the reference distance dref from the object capturing device 20, ascanning angle corresponding to a lateral direction length of 300 mm ofthe reflecting sheet 40, which corresponds to a scanning direction size,is determined as the reference scanning angle range θ_(ref).

Therefore, as illustrated in FIG. 9B, the reference scanning angle rangeθ_(ref) can be determined with a function described below, which usesthe reference distance d_(ref) as a variable.

θ_(ref)=2·tan⁻¹(W/2·d _(ref))

Where, W is a lateral width of the reflecting sheet 40 along a scanningdirection of measurement light. In the present embodiment, as describedabove, as the reference distance d_(ref), an average value of distancesfrom the object capturing device 20 to an object is used.

Furthermore, as illustrated in FIG. 10A, when intensity distribution Iof reflected light detected within the scanning angle range ±Δθcorresponding to a size of the object along the scanning directioncorresponds to reference intensity distribution I_(ref) of reflectedlight from a capture target, the detected object can be identified asthe capture target. That is, as long as a size in a scanning directionof a capture target and intensity distribution of reflected light areset differently from a size in a scanning direction of another objectand intensity distribution of reflected light, the capture target can besurely identified.

As illustrated in FIG. 10B, the reference intensity distribution I_(ref)can be obtained with a function that uses as a variable the distance dfrom the object capturing device 20 to the reflecting sheet 40. Thedistance d and the intensity I of reflected light are normally inverselyproportional to a square of the distance d. That is, when the distance dto the reflecting sheet 40 reduces, the intensity I of reflected lightincreases. When the distance d to the reflecting sheet 40 increases, theintensity I of reflected light reduces. That is, reference intensitydistribution can be determined based on a distance to an object.

It is preferable that the reference scanning angle range θ_(ref) and thereference intensity distribution I_(ref) described above be determinedbased on a degree of deviation in a scanning angle range with respect toa reference scanning position of measurement light.

When a capture target lying within a scanning range of measurement lightchanges in angle, a scanning direction size of the capture target andintensity distribution of reflected light change even when referencedistances are equal. Even in such a case, by using, as an index, adegree of deviation in a scanning angle range with respect to areference scanning position of measurement light to determine areference scanning angle range and reference intensity distribution, acapture target can be further surely identified.

As a reference scanning position of measurement light, a scanningstarting point angle (a position where θ=0 degrees in FIG. 9A), ascanning ending point angle (a position where θ=270 degrees in FIG. 9A),or a scanning angle at a center of a scanning range (a position whereθ=135 degrees in FIG. 9A), for example may be arbitrarily selected. Adegree of deviation in scanning angle range may be represented by anangular difference between the reference scanning position describedabove and an angle arbitrarily selected from among a starting pointangle of a scanning angle range (a position where θ=135 degrees−Δθ inFIG. 9A), an ending point angle (a position where θ=135 degrees+Δθ inFIG. 9A), or a central angle (a position where θ=135 degrees in FIG.9A), for example. Based on a function that uses the angular differenceas a variable, the reference scanning angle range θ_(ref) and thereference intensity distribution I_(ref) may be respectively determined.

Furthermore, it is preferable that the reference scanning angle rangeθ_(ref) and the reference intensity distribution I_(ref) be determinedbased on an inclination angle of a capture target (reflecting sheet 40)with respect to the optical axis of measurement light, which isdetermined based on distances within a scanning angle range.

Depending on an inclination angle of a capture target (reflecting sheet40) with respect to the optical axis of measurement light, even when thereference distances d_(ref) are equal, a scanning direction size of thecapture target and intensity distribution of reflected light change.Even in such a case, based on distances within a scanning angle range,an inclination of a capture target (reflecting sheet 40) with respect tothe optical axis of measurement light is obtained. Based on the obtainedinclination angle of the capture target (reflecting sheet 40) todetermine the reference scanning angle range θ_(ref) and the referenceintensity distribution I_(ref), the capture target can be further surelyidentified.

FIG. 9C illustrates distances within a scanning angle range, which areeach obtained in a case where a reflection surface of a capture targetis inclined at an angle φ with respect to the optical axis ofmeasurement light. The inclination angle φ can be geometrically obtainedbased on distances to both ends along a scanning direction of areflection surface present within a scanning angle range of a capturetarget. Average values of the distances within the scanning angle rangecan be calculated as reference distances d1, d2, and d3. By using, forexample, a mathematical expression described below, a function that usesas variables the obtained reference distance d_(ref) and the obtainedinclination angle φ, the scanning angle range θ_(ref) can be obtained.

θ_(ref)=2·tan⁻¹(W·cos θ/4·d _(ref))

FIG. 10C illustrates various kinds of intensity I of reflected lightwithin a scanning angle range, which are each obtained in a case where areflection surface of a capture target is inclined at an angle φ withrespect to the optical axis of measurement light. Similar to FIG. 9C, byusing the function that uses as variables the obtained referencedistance d_(ref) and the obtained inclination angle φ, the referenceintensity distribution θ_(ref) can be obtained.

The reference scanning angle range θ_(ref) and the reference intensitydistribution I_(ref) described above may be calculated by causing theobject determination unit 82 to perform an arithmetic operation with thefunction described above. The reference distance d_(ref) and theinclination angle φ may be each divided into a plurality of segments.The reference scanning angle range θ_(ref) and the reference intensitydistribution I_(ref) corresponding to each of the segments may be storedin a memory as reference data.

FIG. 11A illustrates an example where the reference intensitydistribution I_(ref) differs depending on reflection properties of thereflecting sheet 40 within a scanning angle range of an incident angleof 0 degrees (vertical incident) ±45 degrees. In a case where thereflecting sheet 40 is a scatterer, such as white paper, intensitydistribution of reflected light detected by the light receiving unit 22presents substantially flat properties even when a scanning angle ofmeasurement light changes.

On the other hand, since, in a case where the reflecting sheet 40 ismade from a metal plate made of aluminum, for example, and has a mirrorsurface, measurement light is reflected by the mirror surface, when themeasurement light is incident on the metal plate in a substantiallyvertical direction, intensity of reflected light detected by the lightreceiving unit 22 becomes greater. Meanwhile, when an incident angle ofthe measurement light shifts from the vertical direction, the intensityof reflected light extremely reduces. The intensity distribution ofreflected light presents such properties that a peak is observed at acentral part, at which the measurement light becomes vertical incident,whereas the intensity gradually lowers around the peak.

In a case where, as the reflecting sheet 40, a recursive reflectingmember is adopted, such intensity distribution can be achieved that,similar to reflected light from a scatterer, such as white paper,intensity is greater enough and expands in a flat shape in a wholeregion. As a recursive reflecting member, for example, such a reflectingsheet is preferably used that is arranged with a trihedron cube cornerelement.

FIG. 11B illustrates intensity distribution of reflected light from areflecting sheet disposed in a posture substantially vertical to theoptical axis of measurement light when a scanning angle is 0 degrees. Ina case where, even when the distance d is constant, a reflection surfaceof a reflecting sheet is a scatter surface, such intensity Ip ofreflected light is observed that transitions in a relatively flat shape.In a case where a reflection surface of a reflecting sheet is a mirrorsurface, such intensity Im of reflected light is observed that isextremely greater at a central part at which the light becomes verticalincident, and that is smaller around both sides. In a case where areflection surface of a reflecting sheet is a recursive reflectingmember, such intensity Is of reflected light is observed thattransitions in a relatively flat shape and is greater than the two kindsof the intensity described above.

FIG. 11C illustrates intensity distribution of reflected light from areflecting sheet slightly inclined from a posture vertical to theoptical axis of measurement light. In a case where a reflection surfaceof a reflecting sheet is a scatter surface, and the reflection surfaceis made from a recursive reflecting member, intensity distributionrarely changes, compared with FIG. 11B. However, in a case where areflection surface is a mirror surface, intensity distribution greatlychanges depending on an incident angle.

Therefore, by adopting the recursive reflecting sheet 40 havingreflection properties different from reflection properties of an objectthat may lead to an erroneous detection, a capture target can beproperly determined. In addition, by determining whether a capturetarget is present based on the reference scanning angle range θ_(ref)and the reference intensity distribution I_(ref) that are reflected withthe property of the reflecting sheet 40, the capture target can beappropriately captured even when the capture target takes any posturewithin a scanning range of measurement light.

FIG. 12 illustrates a flow of an object capturing procedure executed bythe object determination unit 82.

The object determination unit 82 obtains pieces of position data andcorresponding scanning angles which are calculated by the distancecalculation unit 81 per one scan of measurement light and corrected bythe correction calculation unit 83 (S1). Then the object determinationunit 82 performs object determination processing configured to recognizean object from which the position data is obtained as a candidate of acapture target, when a continuous scanning angle range, within which adifference between a scanning angle and each of distances at scanningangles adjacent to the scanning angle is determined to be equal to orless than a predetermined threshold value, is equal to or more than apredetermined threshold value, based on the plurality of position data(S2)

Per an object being extracted, a reference distance is calculated (S3).The function described above is used to calculate a reference scanningangle range (S4). The function described above is used as well tocalculate reference intensity distribution (S5). Such a configurationmay be applied that a reference scanning angle range and referenceintensity distribution are determined beforehand in accordance with areference distance and a degree of deviation from a scanning anglecorresponding to the reference distance, i.e., a degree of deviationfrom a reference scanning angle, and that data stored in a memory isread.

A difference between a scanning angle range and the reference scanningangle range of each object is obtained. When the difference is equal toor less than a predetermined threshold value, it is determined that theobject is likely to be the capture target. When the difference is morethan the predetermined threshold value, it is determined that the objectis not the capture target (S6, OK).

Next, for the object determined in step S6 that the object is likely tobe the capture target, a difference between intensity distribution ofreflected light and the reference intensity distribution is obtained.When the difference is equal to or less than a predetermined thresholdvalue, it is determined that the object is the capture target (S7, OK).

When the reference distance to the object that is determined as thecapture target is equal to or less than a predetermined proximitythreshold value (S8, Y), a deceleration or stop warning signal is outputto the traveling control unit 70 (see FIG. 8). Such a configuration maybe applied that two stages, i.e., greater and smaller, of proximitythreshold values are set. In this case, when a value equal to or lessthan the greater threshold value is determined, a deceleration warningsignal may be output. Meanwhile, when a value equal to or less than thesmaller threshold value is determined, a stop warning signal may beoutput.

When, in step S8, the reference distance of the capture target isgreater than the predetermined proximity threshold value, and adeceleration or stop warning signal has been output in the past, thesignal is cancelled. Steps S1 to S9 described above are repeated perunit scan of measurement light.

[Object Determination Device According to Second Embodiment]

In the object determination device 20 described above, the lightemission unit 21 includes the infrared laser diode. However, thewavelength is not particularly limited. The light emission unit mayinclude a plurality of light sources respectively configured to emitlight at wavelengths different from each other. The reference intensitydistribution I_(ref) described above may be respectively determined bythe wavelengths of the light sources. A number of the light sources andwavelengths of light emitted from the light sources are not particularlylimited, but may be appropriately set. The reference scanning anglerange θ_(ref) may be appropriately set as well.

For example, in a case where the light emission unit includes two lightsources, such as a red laser diode chip and a green laser diode chip,and reference intensity distribution is set per each of wavelengths ofthe light sources in accordance with spectral reflection properties of areflecting sheet serving as a reflection surface of a capture target,which differ from spectral reflection properties of a surface of anobject other than the reflection surface of the capture target, thecapture target can be further surely identified.

For example, spectral reflection properties of a reflecting sheet may beset to allow two kinds of reference intensity distribution with respectto red and green to be identical in properties to each other. Otherwise,spectral reflection properties of a reflecting sheet may be set to allowtwo kinds of reference intensity distribution with respect to red andgreen to differ in properties from each other. Along a scanningdirection of measurement light, kinds of spectral reflection propertieswith respect to red and green may be set to differ from each other in acontinuous manner or in a stepwise manner.

In this case, the light emission control unit 84 (see FIG. 8) mayalternately switch and drive the two light sources during a scanningperiod of the light scanning unit 23. In a case where a moving speed ofa capture target is fully slower than a speed corresponding to ascanning period of the light scanning unit 23, the light sources can beswitched and driven per scanning period.

Instead of a configuration where the light emission unit 21 of theobject determination device 20 includes a plurality of light sourcesrespectively configured to emit light at wavelength different from eachother, a plurality of the object determination devices 20 each includinga light emission unit including a light source may be prepared, and thelight sources of the light emission units of the object determinationdevices 20 may be respectively configured to emit light at wavelengthsdifferent from each other.

FIG. 14 illustrates another example of the light scanning unit 23 of theobject determination device 20. In the light guide unit 54 assembled inthe light scanning unit 23, at positions facing the light emission unit21, the polarizer PL described above is disposed at an inlet end of themeasurement light optical path L. Meanwhile, the analyzer AN describedabove is disposed at an outlet end of the reflected light optical pathL2 for reflected light polarized by the deflecting mirror 52 to achieveintegral rotation with the deflecting mirror 52.

In a case where the configuration in FIG. 7 is adopted, weights of thepolarizer PL and the analyzer AN slightly increase torque about therotating shaft 51, increasing power of the motor 50. However, stablerotation of the light scanning unit 23 can be achieved. Even when theconfiguration in FIG. 14 is adopted, an increase in power of the motor50 is not so greater than an increase in power achieved in theconfiguration in FIG. 7.

FIG. 15 illustrates another example including the light scanning unit 23of the object determination device 20. In each of the examples in FIGS.7 and 14, in the light emission direction, the ¼ wavelength plate 28 isdisposed at a position immediately behind the light projection lens 24.However, in the example in FIG. 15, a polarizer PL′ for linearpolarization is further disposed between the light emission unit 21 andthe ¼ wavelength plate 28. The polarizer PL serves as a first polarizer.The polarizer PL′ serves as a second polarizer.

By adjusting the polarizer PL′ to allow a polarization surface toreceive incident light at a bearing angle of 45 degrees relative to afast axis (or slow axis) of the ¼ wavelength plate 28, linearlypolarized light can turn into circularly polarized light forming asubstantially perfect circle. As a result, with the polarizer PLprovided in the light scanning unit 23, measurement light appropriatelylinearly polarized can be obtained.

In a case where the polarizer PL′ is not provided, but such a lens thatis made of a resin having greater birefringence, such as polycarbonate,is used as the light projection lens 24, a polarization state ofmeasurement light emitted from the laser diode constituting the lightemission unit 21 changes. In this case, measurement light passingthrough the ¼ wavelength plate 28 turns into circularly polarized lighthaving an almost ellipse shape. Measurement light passed through thepolarizer PL then turns into elliptically polarized light. As a result,accuracy in detecting reflected light may lower. However, with thepolarizer PL′, measurement light emitted from the laser diode can besurely linearly polarized and guided to the ¼ wavelength plate 28. Aswell as measurement light passed through the polarizer PL can beappropriately linearly polarized. Therefore, accuracy in detectingreflected light can be increased.

FIG. 16 illustrates another example including the light scanning unit 23of the object determination device 20. On an outlet side of the lightguide unit 54 assembled in the light scanning unit 23, a polarizer PL″having polarization properties identical in direction to thepolarization properties of the polarizer PL is disposed identically ininclined posture to the deflecting mirror 52.

In a case where the polarizer PL″ is not provided, and an object to beirradiated with measurement light lies adjacent to the objectdetermination device 20, a diameter of a measurement light beam emittedfrom the light guide unit 54 reduces. As well as a degree of expansionof a reflected light beam from the object reduces. As a result, adiameter of reflected light advancing in the reflected light opticalpath L2 becomes closer to a diameter of the measurement light opticalpath L1. As well as, a quantity of light guided to the light receivingunit 22 reduces. In this case, such a situation may occur that adistance is not precisely detected.

Even in such a case, by providing the polarizer PL″, in reflected lightfrom the object, linearly polarized light perpendicular to linearlypolarized light of measurement light is reflected by the polarizer PL″,and is guided to the light receiving unit 22.

Therefore, when the object is a capture target, linearly polarized lightperpendicular to linearly polarized light of measurement light is guidedto the light receiving unit 22, increasing detection accuracy. When theobject is not the capture target, reflected light of linearly polarizedlight identical to linearly polarized light of measurement light canpass through the polarizer PL″. Therefore, a quantity of reflected lightto be guided to the light receiving unit 22 reduces, making it possibleto avoid erroneous detection. That is, the polarizer PL″ functions as ahalf mirror configured to guide, to the light receiving unit 22,reflected light that is incident on the light guide unit 54. As long assuch a condition is satisfied that reflected light is guided to thelight receiving unit 22, the polarizer PL″ can be provided as requiredin the measurement light optical path L1. In some cases, an ordinaryhalf mirror can be used.

[Filtering Processing of Identifying Capture Target Based on LightReceiving Level of Reflected Light]

An improvement on an algorithm for identifying a capture target by theobject determination unit 82 (see FIG. 8) will be described.

FIG. 17A illustrates, in a case where the object determination device 20having the configuration illustrated in FIG. 16 is used, distances withrespect to various reflecting members and properties of detecting alight receiving level of reflected light. FIG. 18 illustrates materialsof the reflecting members illustrated in FIG. 17A. The “reflectingplate” illustrated in FIG. 18 is applied to a capture target to serve asa reflecting plate made from an optical member described above (e.g., areflecting plate using a trihedron cube corner element).

In a case where a distance ranges from 50 mm to 1000 mm inclusive, alight receiving level by the reflecting plate described above is greaterenough than that of other reflecting members. In a case where a distanceexceeds 1000 mm, a light receiving level by the reflecting plate greatlylowers, but is still a greater value, compared with the other reflectingmembers.

Therefore, by setting, for a light receiving level of reflected light, athreshold value in accordance with a distance, a true capture target canbe determined when reflected light is received at a level exceeding athreshold value. That is, by setting different threshold values forlevels of receiving reflected light in accordance with detectiondistances, a capture target and other objects can be identified.

Specifically, a threshold value for a light receiving level of reflectedlight at a shorter distance may be set greater than a threshold valuefor a light receiving level of reflected light at a longer distance. Inthe example described above, a boundary distance between the shorterdistance and the longer distance is approximately 1000 mm. At a shortdistance equal to or shorter than 1000 mm, a threshold value of 1000 isset. At a long distance longer than 1000 mm, a threshold value of 700 isset.

The value of the boundary between the short distance and the longdistance can be set to an appropriate value as required in accordancewith a specific configuration of the object determination device 20,such as a quantity of light emitted from a light source, sensitivity ofa light-receiving element, and a configuration of an optical system.Such a configuration can be applied that threshold values are switchedin a multi-stepwise manner. For example, different threshold values arerespectively set at boundaries among a short distance, a mediumdistance, and a long distance.

Setting of switching threshold values for levels of receiving reflectedlight based on a detection distance to an object is effective in notonly the object determination device 20 configured as illustrated inFIG. 16, but also the object determination device 20 configured asillustrated in FIGS. 7, 14, and 15.

FIG. 17B illustrates properties of detecting reflected light in a casewhere an angle θ1 between the optical axis of measurement light and anormal line to the reflecting plate is altered within a range of 0degrees ±45 degrees. Such a tendency is illustrated that, when the angleθ1 is 0 degrees, the light receiving level becomes maximum, whereas,when the angle θ1 is around ±45 degrees, the light receiving levelbecomes minimum. When the angle θ1 is around ±45 degrees, the lightreceiving level is equal to or less than the threshold value for shortdistance of 1000. In this case, no detection may be possible when theangle θ1 of the reflecting plate is around 45 degrees.

FIG. 17C illustrates a light receiving level of reflected light along ascanning direction in a case where the angle θ1 is set to 0 degrees withrespect to various reflecting members. In FIG. 17C, STEP 540 representsa light receiving level in a case where a scanning direction ofmeasurement light aligns with a normal line direction to a reflectingmember. A distance between the reflecting member and the objectdetermination device 20 is 500 mm. When the threshold value for thelight receiving level is set to 1000, the reflecting plate and otherreflecting members can be explicitly identified.

FIG. 17D illustrates light receiving levels of reflected light along ascanning direction in a case where the angle θ1 with respect to thereflecting plate is set to 0 degrees, −45 degrees, and +45 degrees. Adistance between the reflecting plate and the object determinationdevice 20 is 500 mm. Similar to FIG. 17B, by setting a threshold valuefor the light receiving level to a threshold value for short distance of1000, no detection may be possible when the angle θ1 is around ±45degrees. Even in such a case, by providing a second threshold value forshort distance at a level lower than a level of the threshold value forshort distance, and setting the value to 700, for example, a securedetection becomes possible even when the angle θ1 is around ±45 degrees.

However, when the second threshold value for short distance is set to700, as illustrated in FIG. 17A, and when the angle θ1 is around 0degrees, a mirror reflecting member, such as an aluminum plate or an SUSplate, may be erroneously detected as a reflecting plate of a capturetarget.

Even in such a case, by taking into account a number of steps ofcontinuously detecting reflected light relative to a scanning directionof measurement light, reflected light from the mirror reflecting memberand reflected light from the reflecting plate (e.g., reflecting plateusing a trihedron cube corner element) can be identified.

For example, as illustrated in FIG. 17C, by setting a threshold numberof steps greater than a number of steps of continuously detectingreflected light from the mirror reflecting member, which is detectedwhen the angle θ1 is 0 degrees and the second threshold value for shortdistance is 700, when a light receiving level of reflected light iscontinuously observed at values equal to or more than the secondthreshold value for short distance of 700 in a number of steps equal toor more than the threshold number of steps, a capture target having thereflecting plate can be identified.

For example, in a case where a detection distance is a short distance,under either of a condition that a light receiving level of reflectedlight is equal to or more than a threshold value for short distance or acondition that a light receiving level of reflected light iscontinuously observed at values equal to or more than a second thresholdvalue for short distance in a number of steps equal to or more than athreshold number of steps, a capture target can be identified.

In a case where a detection distance is a long distance, by separatelyproviding a second threshold value for long distance at a level smallerthan a level of a threshold value for long distance, under either acondition that a light receiving level of reflected light is equal to ormore than the threshold value for long distance or a condition that alight receiving level of reflected light is continuously observed atvalues equal to or more than the second threshold value for longdistance in a number of steps equal to or more than the threshold numberof steps, a capture target can be identified.

[Light Scanning Unit Assembled in Object Determination Device Accordingto Other Embodiments]

The object capturing device 20 illustrated in FIG. 7 and described aboveincludes, as an example, the light scanning unit 23 including the motor50 provided on the inner wall of the upper surface of the upper casing20B and the deflecting mirror 52 fixed to the rotating shaft 51 of themotor 50 to be integrally rotatable with the rotating shaft 51. However,a configuration of a light scanning unit of an object capturing device,to which the present invention is applied, is not limited to theconfiguration described above. Another known configuration of a lightscanning unit can be adopted.

For example, instead of the deflecting mirror described above, such arotating polygon mirror may be used that rotates, about a longitudinalshaft center, a polygonal prism having side surfaces respectively formedinto mirror surfaces to allow the light emission unit to emitmeasurement light to a measurement target space to perform scanning, aswell as to guide reflected light to the light receiving unit.

Instead of the scanning mechanism that rotates the flat deflectingmirror, as described above, such a swing mechanism may be adopted thatperforms scanning in a swinging manner. Such a configuration may beadopted that a swing mechanism configured to allow a deflecting mirrorrotated and driven by the light scanning unit 23 to swing about a shaftcenter intersecting with a rotating shaft center to perform scanning, asdescribed above, is further provided to achieve three-dimensionalscanning.

Even in any aspects, a light scanning unit may include a deflectingmirror and a light guide unit defining an optical path configured toguide measurement light polarized by the deflecting mirror to ameasurement target space and an optical path configured to guidereflected light to a light receiving unit. Furthermore, a polarizer maybe disposed on a measurement light optical path side of the light guideunit. Meanwhile, an analyzer may be disposed on a reflected lightoptical path side of the light guide unit.

With the configuration described above, the light guide unit definesregions of optical paths into the measurement light optical path and thereflected light optical path. When measurement light emitted from thelight emission unit advances into the measurement light optical path,only linearly polarized light vibrating in the first direction passesthrough the polarizer to reach a measurement target space to achievescanning. When reflected light from an object advances into thereflected light optical path, only linearly polarized light vibrating inthe second direction perpendicular to the first direction passes throughthe analyzer. The reflected light is then received by the lightreceiving unit.

[Signal Processing of Reducing Effects of Interference Light From OtherObject Determination Devices]

When measurement light from other ones of the object capturing devices20 present around one of the object capturing devices 20 is incident asinterference light, the light may be erroneously detected as reflectedlight with respect to the measurement light emitted from the one of theobject capturing devices 20. In a case where periods at whichmeasurement light is emitted from two of the object capturing devices 20are identical to each other, interference light is incident at anidentical period, possibly leading to an erroneous detection.

With a configuration of the light emission control unit 84 (see FIG. 8),where average periods at which measurement light is emitted from theobject capturing devices 20 are kept constant, but emission periods areshifted at random within a range of a T/2 periods around an averageperiod T, such a phenomenon can be avoided that interference light isincident at an identical period.

It is preferable that the distance calculation unit 81 (see FIG. 8) beconfigured, in a case where a plurality of reflected lights are detectedwith respect to one pulse of measurement light emitted from each of theobject capturing devices 20, to execute processing of dividing theperiod T of measurement light into a plurality of time domains, and ofstoring, in a memory, that a detected reflected light belongs to whichof the time domains, on a predetermined, continuous number ofmeasurement lights to adopt, as true reflected light, reflected light inone of the time domains, in which a number of detected reflected lightsis maximum.

Similarly, the object determination unit 82 (see FIG. 8) may beconfigured, in a case where a plurality of reflected lights are detectedwith respect to one pulse of measurement light emitted from each of theobject capturing devices 20, to cause the distance calculation unit 81(see FIG. 8) to calculate a distance with respect to each of thereflected lights, and to execute processing of dividing the period T ofmeasurement light into a plurality of time domains, and of storing, in amemory, that a detected distance belongs to which of the time domains,on a predetermined, continuous number of measurement lights to adopt, asa distance with respect to true reflected light, a distance observedfrom one of the time domains, in which a number of detected distances ismaximum.

Furthermore, the distance calculation unit 81 (see FIG. 8) may beconfigured, in a case where a plurality of reflected lights are detectedwith respect to one pulse of measurement light emitted from each of theobject capturing devices 20, to execute processing of dividing theperiod T of measurement light into a plurality of time domains, and tostore, in a memory, that a detected reflected light belongs to which ofthe time domains, for a predetermined number of scanning periods toadopt, as a distance with respect to true reflected light, a distanceobserved from one of the time domains, in which a number of detectedreflected lights is maximum.

Similarly, the object determination unit 82 (see FIG. 8) may beconfigured, in a case where a plurality of reflected lights are detectedwith respect to one pulse of measurement light emitted from each of theobject capturing devices 20, to cause the distance calculation unit 81(see FIG. 8) to calculate a distance with respect to each of thereflected lights, and to execute processing of dividing the period T ofmeasurement light into a plurality of time domains, and of storing, in amemory, that a detected distance belongs to which of the time domains,for a predetermined number of scanning periods to adopt, as a distancewith respect to true reflected light, a distance observed in one of thetime domain, in which a number of detected distances is maximum.

[Reflection Surface of Capture Target]

It is preferable that a capture target to be captured by each of theobject capturing devices 20 described above include the reflecting sheet40 having reflection properties causing a quantity of reflected lightalong a scanning direction of measurement light used for scanning by thelight scanning unit 23 to change in a stepwise manner.

By setting reflection properties of a reflection surface of a capturetarget to allow a quantity of reflected light along a scanning directionof measurement light used for scanning by the light scanning unit 23 tochange in a stepwise manner or in a continuous manner, identification athigher accuracy from another object without having such properties canbe achieved.

For example, as illustrated in FIG. 19A, with the reflecting sheet 40set with surface reflectivity that is higher in areas at the both endsand the central part of the reflecting sheet 40, but that is lower inareas between the both ends and the central part along a scanningdirection of measurement light, which causes a quantity of reflectedlight detected by the light receiving unit 22 along the scanningdirection to change in a stepwise manner, reflected light from otherobjects can be surely identified.

For example, as illustrated in FIG. 19B, with the reflecting sheet 40set with surface reflectivity changing in a saw-tooth manner along ascanning direction of measurement light, which causes a quantity ofreflected light detected by the light receiving unit 22 along thescanning direction to increase or decrease in a continuous manner,reflected light from other objects can be surely identified.

The reflecting sheet 40 having such reflection properties may be adoptedthat cause spectral reflection properties with respect to a wavelengthof measurement light along a scanning direction of the measurement lightto change in a stepwise manner or in a continuous manner. In a casewhere the light emission unit 21 includes a plurality of light sourcesconfigured to emit light at different wavelengths, it is preferable thatsuch reflection properties be provided that spectral reflectionproperties change per the wavelength of each of the light sources.

In any case, it is preferable that, as the reflecting sheet 40, arecursive reflecting member, in particular, a recursive reflectingmember arranged on its surface with a trihedron cube corner element, beused. In a case where such a recursive reflecting member is used, thereflecting mirrors 41, 42, and 43 (See FIG. 14A) can be each formed withan interference film at a predetermined thickness to adjust spectralreflection properties.

Instead of providing a recursive reflecting member in a whole area, thewhole area of the reflecting sheet 40 may be divided into regions eachprovided with a recursive reflecting member and regions each notprovided with a recursive reflecting member to cause a quantity ofreflected light along a scanning direction of measurement light tochange in a stepwise manner or in a continuous manner. For example, in aregion without a recursive reflecting member, a scattering reflectingmember or a light absorbing member may be provided.

By appropriately combining the object capturing device 20 and thereflecting sheet 40 provided to a capture target, according to theplurality of aspects described above, an object capturing systemaccording to the present invention is achieved.

Any embodiments described above are merely examples of the presentinvention, and the scope of the present invention is not limited to thisdescription. Specific configurations of the components can be changed asappropriate as long as the advantageous effects of the present inventioncan be provided.

DESCRIPTION OF SYMBOLS

-   1: manufacturing device-   5: traveling rail-   10: carrying cart-   20: object capturing device-   21: light emission unit-   22: light receiving unit-   23: light scanning unit-   24: light projection lens-   25: light receiving lens-   40: reflecting sheet-   54: light guide unit-   70: traveling control unit-   80: control unit-   81: distance calculation unit-   82: object determination unit-   100: manufacturing facility-   AN: analyzer-   PL, PL′, PL″: polarizer

1-7. (canceled)
 8. An object capturing device configured to capture anobject present in a measurement target space, the object capturingdevice comprising: a light emission unit; a light receiving unit; alight scanning unit configured to cause measurement light emitted at apredetermined wavelength from the light emission unit to head toward ameasurement target space to perform scanning, and to guide reflectedlight from an object present in the measurement target space withrespect to the measurement light to the light receiving unit; apolarization filter disposed in the light scanning unit, thepolarization filter including a polarizer configured to allow only lightvibrating in a first direction in the measurement light to transmit, andan analyzer configured to allow only light vibrating in a seconddirection perpendicular to the first direction in the reflected light totransmit; a circular polarizing plate disposed between the lightemission unit and the polarizer; and a second polarizer disposed betweenthe light emission unit and the circular polarizing plate.
 9. The objectcapturing device according to claim 8, wherein the light scanning unitcomprises a polarization mirror, and a light guide unit defining anoptical path configured to guide measurement light polarized by thepolarization mirror to the measurement target space and an optical pathconfigured to guide the reflected light to the light receiving unit, andwherein the polarizer is disposed on a measurement light optical pathside of the light guide unit, and the analyzer is disposed on areflected light optical path side of the light guide unit.
 10. An objectcapturing device configured to capture an object present in ameasurement target space, the object capturing device comprising: alight emission unit; a light receiving unit; and a light scanning unitconfigured to cause measurement light emitted at a predeterminedwavelength from the light emission unit to head toward a measurementtarget space to perform scanning, and to guide reflected light from anobject present in the measurement target space with respect to themeasurement light to the light receiving unit, wherein the lightscanning unit includes a light guide unit defining an optical pathconfigured to guide measurement light polarized by a polarization mirrorto the measurement target space and an optical path configured to guidethe reflected light to the light receiving unit, and wherein a halfmirror configured to guide the reflected light to the light receivingunit is disposed on a measurement light optical path side of the lightguide unit.
 11. The object capturing device according to claim 8,wherein the object capturing device comprises a casing, and wherein thecasing has a part serving as a path for the measurement light and thereflected light, the part being configured to allow the measurementlight to transmit, the part being made of a material having lowpolarization properties with respect to the measurement light.
 12. Theobject capturing device according to claim 9, wherein the objectcapturing device comprises a casing, and wherein the casing has a partserving as a path for the measurement light and the reflected light, thepart being configured to allow the measurement light to transmit, thepart being made of a material having low polarization properties withrespect to the measurement light.
 13. The object capturing deviceaccording to claim 10, wherein the object capturing device comprises acasing, and wherein the casing has a part serving as a path for themeasurement light and the reflected light, the part being configured toallow the measurement light to transmit, the part being made of amaterial having low polarization properties with respect to themeasurement light.
 14. The object capturing device according to claim 8,wherein the light emission unit comprises a plurality of light sourcesconfigured to emit light at different wavelengths, the light emissionunit being switched and driven in synchronization with a scanning cycleof the light scanning unit.
 15. The object capturing device according toclaim 9, wherein the light emission unit comprises a plurality of lightsources configured to emit light at different wavelengths, the lightemission unit being switched and driven in synchronization with ascanning cycle of the light scanning unit.
 16. The object capturingdevice according to claim 10, wherein the light emission unit comprisesa plurality of light sources configured to emit light at differentwavelengths, the light emission unit being switched and driven insynchronization with a scanning cycle of the light scanning unit. 17.The object capturing device according to claim 11, wherein the lightemission unit comprises a plurality of light sources configured to emitlight at different wavelengths, the light emission unit being switchedand driven in synchronization with a scanning cycle of the lightscanning unit.